The 9/11 attack killed a lot more people, disrupted major markets, cost the economy billions. That is a large scale attack.
A boat carrying 10 men armed with 40 mm grenade launchers with thermite or WP grenades and machine guns attacking an oil pumping station or refinery would be far more damaging to America than a boat load of explosives running into a ship or a bridge.
true but a small boat next to a large tanker at a fuel loading dock could be worse.